Heat treated profile extruded hook

ABSTRACT

A method for forming a unitary polymeric projection or fastener comprising a thin, strong flexible backing, and a multiplicity of thin spaced hook members projecting from the upper surface of the unitary backing the method generally including extruding a thermoplastic resin through a die plate which die plate is shaped to form a base layer and spaced ridges, ribs or hook elements projecting above a surface of the base layer. When the die forms the spaced ridges or ribs the cross sectional shape of the hook members are formed by the die plate while the initial hook member thickness is formed by transversely cutting the ridges at spaced locations along their lengths to form discrete cut portions of the ridges. Subsequently longitudinal stretching of the backing layer (in the direction of the ridges on the machine direction) separates these cut portions of the ridges, which cut portion then form spaced apart hook members. The extruded hook members or cut rib hook members are then heat treated resulting in shrinkage of at least a portion of at least the hook head portion thickness by from 5 to 90 percent, preferably 30 to 90 percent.

This is a continuation-in-part of application Ser. No. 10/411,042, filedApr. 10, 2003, now abandoned which is a continuation-in-part ofapplication Ser. No. 10/316,686, filed Dec. 11, 2002 (now abandoned),which is a continuation-in-part of application Ser. No. 10/214,051,filed Aug. 7, 2002 (now abandoned), which is a continuation-in-part ofapplication Ser. No. 10/050,403, filed Jan. 15, 2002 (now abandoned),the disclosures of which are incorporated herein by reference.

BACKGROUND AND SUMMARY

The present invention concerns molded hook fasteners for use with hookand loop fasteners.

BACKGROUND OF THE INVENTION

There are a variety of methods known to form hook materials for hook andloop fasteners. One of the first manufacturing methods for forming hooksinvolved weaving loops of monofilaments into a fibrous or film backingor the like followed by cutting the filament loops to form hooks. Thesemonofilament loops were also heated to form headed structures such asdisclosed in U.S. Pat. Nos. 4,290,174; 3,138,841 or 4,454,183. Thesewoven hooks are generally durable and work well for repeated uses.However, they are generally expensive and coarse to the touch.

For use in disposable garments and the like, it was generally desirableto provide hooks that were inexpensive and less abrasive. For these usesand the like, the solution was generally the use of continuous extrusionmethods that simultaneously formed the backing and the hook elements, orprecursors to the hook elements. With direct extrusion molding formationof the hook elements, see for example U.S. Pat. No. 5,315,740, the hookelements must continuously taper from the backing to the hook tip toallow the hook elements to be pulled from the molding surface. Thisgenerally inherently limits the individual hooks to those capable ofengaging only in a single direction while also limiting the strength ofthe engaging head portion of the hook element.

An alternative direct molding process is proposed, for example, in U.S.Pat. No. 4,894,060, which permits the formation of hook elements withoutthese limitations. Instead of the hook elements being formed as anegative of a cavity on a molding surface, the basic hook cross-sectionis formed by a profiled extrusion die. The die simultaneously extrudesthe film backing and rib structures. The individual hook elements arethen formed from the ribs by cutting the ribs transversely followed bystretching the extruded strip in the direction of the ribs. The backingelongates but the cut rib sections remain substantially unchanged. Thiscauses the individual cut sections of the ribs to separate each from theother in the direction of elongation forming discrete hook elements.Alternatively, using this same type extrusion process, sections of therib structures can be milled out to form discrete hook elements. Withthis profile extrusion, the basic hook cross section or profile is onlylimited by the die shape and hooks can be formed that extend in twodirections and have hook head portions that need not taper to allowextraction from a molding surface. This is extremely advantageous inproviding higher performing and more functionably versatile hookstructures. However, a limitation with this method of manufacture is informing hook structures that are extremely narrow in the extrusiondirection of the ribs or the cut direction. Cutting the formed ribs atvery closely spaced intervals is difficult at commercially acceptableproduction speeds. Further, when the cut length is extremely closelyspaced the previously cut portions of the ribs tend to fuse due to theheat created by the cutting operation. As such, there is a need toimprove this process so as to allow for production of narrower hookprofiles and formation of the narrower hook profiles at commerciallyacceptable production speeds.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides a method for forming preferably a unitarypolymeric hook fastener comprising a thin, strong flexible backing, anda multiplicity of thin, spaced hook members projecting from the uppersurface of the unitary backing. The method of the invention generallycan be used to form thin upstanding projections, which may or may not behook members that project upwardly from the surface of a unitary filmbacking of at least a uniaxially oriented polymer. The hook members eachcomprise a stem portion attached at one end to the backing, and a headportion at the end of the stem portion opposite the backing. The headportion can also extend from a side of a stem portion or be omittedentirely to form alternative projections which can be other forms than ahook member. For hook members, the head portion preferably projects pastthe stem portion on at least one of two opposite sides. At least thehook head portions have been heat treated so as to decrease the hookhead thickness and thereby reducing or eliminating molecular orientationin at least the hook head in the machine direction. Generally, the hookmembers suitable for use in the invention method, both before and aftertreatment, have a height dimension from the upper surface of the backingof less than 5000 μm. The stem and head portions generally have athickness dimension of less than 1500 82 m in a first direction parallelto the surfaces of the backing. The stem portions each have a widthdimension in the range of 50 to 500 μm in a second direction, generallyat a right angle to the first direction and parallel to the surfaces ofthe backing, and the head portions each have a width dimension in thesecond direction that is between 50 and 2000 μm greater than the widthdimension of the stem portion and a total width of less than 5000 μm.There are generally at least 10, preferably 20 to 200 or 20 to 300 hookmembers per square centimeter of the base.

The fastener is preferably made by a novel adaptation of a known methodof making hook fasteners as described, for example, in U.S. Pat. Nos.3,266,113; 3,557,413; 4,001,366; 4,056,593; 4,189,809 and 4,894,060 oralternatively 6,209,177, the substance of which are incorporated byreference in their entirety. The preferred method generally includesextruding a thermoplastic resin through a die plate which die plate isshaped to form a base layer and spaced ridges, ribs or hook elementsprojecting above a surface of the base layer. These ridges generallyform the cross-section shapes of the desired projection to be produced,which is preferably a hook member. When the die forms the spaced ridgesor ribs the cross sectional shape of the hook members are formed by thedie plate while the initial hook member thickness is formed bytransversely cutting the ridges at spaced locations along their lengthsto form discrete cut portions of the ridges. Subsequently longitudinalstretching of the backing layer (in the direction of the ridges on themachine direction) separates these cut portions of the ridges, which cutportion then form spaced apart hook members. The extruded hook membersor cut rib hook members are then heat treated resulting in shrinkage ofat least a portion of at least the hook head portion thickness by from 5to 90 percent, preferably 30 to 90 percent. In an alternativeembodiment, the heat treatment is continued to likewise shrink at leasta portion of the stem portion of the hook members. The resulting heattreated projections, preferably hooks, are substantially upstanding orrigid such that they do not droop toward the base layer or are able topenetrate a fibrous or like substrate. In a particular preferredembodiment, the extruded thermoplastic resin contains an immisciblephase to increase the extent of molecular orientation in thethermoplastic polymer or increase the degree of hook member orprojection shrinkage when heat treated.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further described with reference to theaccompanying drawings wherein like reference numerals refer to likeparts in the several views, and wherein:

FIG. 1 schematically illustrates a method for making the hook fastenerportion of FIG. 4.

FIGS. 2 and 3 illustrate the structure of a strip at various stages ofits processing in the method illustrated in FIG. 1.

FIG. 4 is an enlarged perspective view of a hook fastener.

FIGS. 5 a and 5 b are enlarged fragmentary side and end views,respectively, of one hook member in the hook fastener portion of FIG. 4.

FIGS. 6 a and 6 b are views of FIGS. 5 a and 5 b, respectively, afterlimited heat treating of the hook member.

FIGS. 7 a and 7 b are views of FIGS. 5 a and 5 b, respectively, afterheat treating of the entire hook member.

FIGS. 8 and 9 are enlarged fragmentary sectional views of alternateembodiments of hook portions that can be used in hook fastener portionsaccording to the present invention;

FIG. 10 is an alternative embodiment of individual extruded hookelements that can be heat treated in accordance with the inventionmethod.

FIG. 11 is a cross-sectional view of a fully heat treated alternativehook member in accordance with the invention.

FIG. 12 is a cross-sectional view of a heat treated hook member inaccordance with the invention.

FIG. 13 is a cross-sectional view of a fully heat treated hook member inaccordance with the invention.

FIG. 14 is a cross-sectional view of a fully heat treated hook member inaccordance with the invention.

FIG. 15 is a perspective view of a disposable garment using a preferredhook member according to the present invention.

FIG. 16 is a perspective view of a disposable garment using a preferredhook member according to the present invention.

FIG. 17 is a perspective view of a disposable garment using a preferredhook member according to the present invention.

FIG. 18 is a perspective view of a feminine hygiene article.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 4 is an exemplary polymeric hook fastener portion,which can be produced, or heat treated according to the presentinvention is generally designated by the reference numeral 10. The hookfastener portion 10 comprises a thin strong flexible film-like backing11 having generally parallel upper and lower major surfaces 12 and 13,and a multiplicity of spaced hook members 14 projecting from at leastthe upper surface 12 of the backing 11. The backing can have planarsurfaces or surface features as could be desired for tear resistance orreinforcement. As is best seen in FIG. 5, the hook members 14 eachcomprise a stem portion 15 attached at one end to the backing 11 andpreferably having tapered sections 16 that widen toward the backing 11to increase the hook anchorage and breaking strengths at their junctureswith the backing 11, and a head portion 17 at the end of the stemportion 15 opposite the backing 11. The sides 34 of the head portion 17can be flush with the sides 35 of the stem portion 15 on two oppositesides. The head portion 17 has hook engaging parts or arms 36, 37projecting past the stem portion 15 on one or both sides 38. The hookmember shown in FIGS. 5 a and 5 b has a rounded surface 18 opposite thestem portion 15 to help the head portion 17 enter between loops in aloop fastener portion. The head portion 17 also has transversecylindrically concave surface portions 19 at the junctures between thestem portion 15 and the surfaces of the head portion 17 projecting overthe backing 11.

With reference to FIGS. 5 a and 5 b, there is shown a singlerepresentative one of the small hook members 14 on which its dimensionsare represented by reference numerals between dimensional arrows. Theheight dimension is 20. The stem and head portions 15 and 17 have athickness dimension 21, which as shown is the same, and the headportions 17 have a width dimension 23 and an arm droop 24. The stemportion has a width dimension 22 at its base before flaring 16 to thebase film 11. The thickness as shown is for a rectilinear shaped hook,with other shapes the thickness can be measured as the shortest distancebetween two opposing sides 34 or 35. Likewise, the width dimension canbe measured as the shortest distance between two opposing sides.

FIGS. 8 and 9 illustrate two of many alternate shapes that could be usedfor the hook members in alternate embodiments of the hook members thatcan be heat treated in accordance with the invention method.

The hook member 25 illustrated in FIG. 8 differs from the hook member 14of FIG. 5 in that its head portion 26 projects farther on opposite sidesfrom its stem portion 27 and is generally uniformly thick so that it canmore easily bend to engage with or disengage from loops on a loopfastener portion.

The hook member 30 illustrated in FIG. 9 differs from the hook member 14of FIG. 5 in that its head portion 31 projects from only one side of itsstem portion 32 and will thus cause significantly greater peel forceswhen peeled away from the direction the head portion 31 projects thanwhen it is peeled toward the direction the head portion 31 projects.

A first embodiment method for forming a hook fastener portion, such asthat of FIG. 4, is schematically illustrated in FIG. 1. Generally, themethod includes first extruding a strip 50 shown in FIG. 2 ofthermoplastic resin from an extruder 51 through a die 52 having anopening cut, for example, by electron discharge machining, shaped toform the strip 50 with a base 53 and elongate spaced ribs 54 projectingabove an upper surface of the base layer 53 that have the crosssectional shape of the hook portions or members to be formed. The strip50 is pulled around rollers 55 through a quench tank 56 filled with acooling liquid (e.g., water), after which the ribs 54 (but not the baselayer 53) are transversely slit or cut at spaced locations along theirlengths by a cutter 58 to form discrete portions 57 of the ribs 54having lengths corresponding to about the desired thicknesses of thehook portions to be formed, as is shown in FIG. 3. The cut can be at anydesired angle, generally from 90° to 30° from the lengthwise extensionof the ribs. Optionally, the strip can be stretched prior to cutting toprovide further molecular orientation to the polymers forming the ribsand/or reduce the size of the ribs and the resulting hook members formedby slitting of the ribs. The cutter 58 can cut using any conventionalmeans such as reciprocating or rotating blades, lasers, or water jets,however preferably it cuts using blades oriented at an angle of about 60to 80 degrees with respect to lengthwise extension of the ribs 54.

After cutting of the ribs 54, the base 53 of the strip 50 islongitudinally stretched at a stretch ratio of at least 2 to 1, andpreferably at a stretch ratio of about 4 to 1, preferably between afirst pair of nip rollers 60 and 61 and a second pair of nip rollers 62and 63 driven at different surface speeds. Optionally, the strip 50 canalso be transversely stretched to provide biaxial orientation to thebase 53. Roller 61 is preferably heated to heat the base 53 prior tostretching, and the roller 62 is preferably chilled to stabilize thestretched base 53. Stretching causes spaces between the cut portions 57of the ribs 54, which then become the hook portions or members 14 forthe completed hook fastener portion 10. The formed hook members are thenheat treated preferably by a non-contact heat source 64. The temperatureand duration of the heating should be selected to cause shrinkage orthickness reduction of at least the head portion by from 5 to 90percent. The heating is preferably accomplished using a non-contactheating source which can include radiant, hot air, flame, UV, microwave,ultrasonics or focused IR heat lamps. This heat treating can be over theentire strip containing the formed hook portions or can be over only aportion or zone of the strip. Or different portions of the strip can beheat treated to more or less degrees of treatment. In this manner, it ispossible to obtain on a single strip hook containing areas withdifferent levels of performance without the need to extrude differentshaped rib profiles. This heat treatment can change hook elementscontinuously or in gradients across a region of the hook strip. In thismanner, the hook elements can differ continuously across a defined areaof the hook member. Further, the hook density can be the same in thedifferent regions coupled with substantially the same film backingcaliper or thickness (e.g., 50 to 500 microns). The caliper can easilybe made the same as the hook strip will have the same basis weight andsame relative amount of material forming the hook elements and backingin all regions despite the difference in the shape of the hooks causedby the subsequent heat treating. The differential heat treatment can bealong different rows or can cut across different rows, so that differenttypes of hooks, such as hooks having different hook thicknesses, can beobtained in a single or multiple rows in the machine direction or thelengthwise direction of the hook strip. The heat treatment can beperformed at any time following creation of the hook element, such thatcustomized performance can be created without the need for modifying thebasic hook element manufacturing process.

FIG. 6 shows a hook member of the FIG. 5 hook after it has been heattreated to cause a reduction in the thickness 21′ of the hook headportion 17′. The other dimensions of the hook member can also changewhich is generally as a result of conservation of mass. The height 20′generally increases a slight amount and the head portion width 23′increases as does the arm droop 24′. The stem and head portions now havea thickness dimension 21′ that is nonuniform and tapers from the base tothe head portion due to the incomplete heat treatment along the entirehook member 14′. Generally the untreated portion has a uniform thicknesscorresponding to the original thickness 21, the generally fully heattreated portion will have a uniform thickness 21′ with a transition zoneseparating the untreated and treated portions. In this embodiment, theincomplete heat treatment also results in variation of the thickness 21′ of the hook head portion from the arm tip to the arm portion adjacentthe stem 15′. All other numbered elements in FIGS. 6 a and 6 bcorrespond to the numbered elements of FIGS. 5 a and 5 b.

Reduction in the hook member thickness is caused by relaxation of atleast the melt flow induced molecular orientation of the hook headand/or stem portion which is in the machine direction, which generallycorresponds to the thickness direction. Also, further reduction inthickness can occur where there is stretch induced molecularorientation, as where the ribs are stretched longitudinally prior tocutting. Melt induced molecular orientation is created by the meltextrusion process as polymer, under pressure and shear forces, is forcedthrough the die orifice(s). The rib or ridge forming sections of the diecreate the molecular orientation in the formed ribs. This molecularorientation extends longitudinally or in the machine direction along theribs or ridges. When the ribs or ridges are cut, the molecularorientation extends generally in the thickness dimension of the cutribs, or cut hook members, however, the molecular orientation can extendat an angle of from about 0 to 45 degrees to the hook member thickness.The initial molecular orientation in the hook members is generally atleast 10 percent, preferably 20 to 100 percent (as defined below). Whenthe hook members are heat treated in accordance with the invention, themolecular orientation of the hook members decrease and the hook memberthickness dimension decreases. The amount of thickness reduction dependsprimarily on the amount of hook member molecular orientation extendingin the machine direction or hook thickness dimension. The heat treatmentconditions, such as time of treatment, temperature, the nature of theheat source and the like can also effect the hook member thicknessreduction. As the heat treatment progresses, the reduction in hookmember, or projection thickness extends from the hook head portion, ortop of the projection, to the stem portion, or down the projection tothe base, until the entire hook member thickness has been reduced.Generally, the thickness reduction is substantially the same in the stemand the hook head portions when both are fully heat treated or partiallyheat treated to the same extent. When only a part of the hook headportion and/or hook head portion and stem portion are heat treated,there is a transition zone where the thickness increases from the upperheat treated portion, generally the head portion, to the substantiallynon-heat treated portion of the stem portion, or stem portion and partof the hook head portion, which have a substantially unreducedthickness. When the thickness dimension shrinks, the width of thetreated portion generally increases, while the overall hook memberheight increases slightly and the arm droop increases. The end result isa hook thickness that can either, not be economically produced directly,or cannot be produced at all by conventional methods. The heat treatedprojection, generally the hook head, and optionally stem, is alsocharacterized by a molecular orientation level of less than 10 percent,preferably less than 5 percent where the base film layer orientation issubstantially unreduced. Generally, the hook member stem or projectionorientation immediately adjacent the base film layer will be 10 percentor higher, preferably 20 percent or higher.

FIG. 7 is a schematic view of a hook member of the FIG. 5 hook, wherethe entire hook member has been subjected to heat treatment. In thiscase, both the hook head portion 17″ and the stem portion 15″ haveshrunk in the thickness direction with corresponding increases in thewidth dimensions 23″ and 22″ and arm droop 24″. In this case, both thestem and head portion have a generally uniform thickness dimension 21″,which is less than the initial hook member width dimension 21. Thetapered section 16″ is generally larger than the initial tapered section16 due the thickness reduction in the stem portion.

The heat treatment is generally carried out at a temperature near orabove the polymer melt temperature. As the heat gets significantly abovethe polymer melt temperature, the treatment time decreases so as tominimize any actual melting of the polymer in the hook head portion ortop of the projection. The heat treatment is carried out at a timesufficient to result in reduction of the thickness of the hook head,and/or stem, but not such that there is a significant deformation of thebacking or melt flow of the hook head portion or top of the projection.Heat treatment can also result in rounding of the hook head portionedges, improving tactile feel for use in garment applications.

Unexpectedly it has been discovered, that for high performance microhookengagement with certain low cost or low loft loop fabrics, that thisheat treatment substantially increases engagement of the microhooks tothe loop fabrics. A particularly preferred novel, microhook memberproducible by the invention method has been discovered where the hookmembers have a height of less than 1000 μm, preferably from 300 to 800μm, and at least a head portion with a thickness of from 50 to 200 μm,preferably 50 to 180 μm. The other dimensions for this improvedmicrohook include a stem width, as defined above, of from 50 to 500 μm,a head portion width of from 100 to 800 μm, and an arm droop of from 50to 700 μm, preferably 100 to 500 μm, and a hook density of at least 50and preferably from about 70 to 150, up to 300, hooks per squarecentimeter. This novel microhook hook portion exhibits improved overallperformance to a variety of low loft loop fabrics.

In certain applications, it has unexpectedly been discovered that verylow hook densities are desirable. For example, hook densities of lessthan 100, preferably less than 70 and even less than 50 hook per squarecentimeter are desirable when used to attach to low loft nonwovens usinga relatively large area flexible hook tab or patch. This low spacing hasbeen found to increase the hooking efficiency of the individual hookelement, particularly relative to low cost and otherwise ineffectivenonwoven materials not traditionally used as loop products. The hook tabor patch can be made flexible by suitable selection of the polymerforming the base layer and/or by stretching the base layer at an angletransverse to the longitudinal stretching. This transverse stretchingcreates biaxial orientation in the base layer reducing its thickness,for example from 20 μm to 100 μm, preferably 30 μm to 60 μm. Biaxialorientation also reduces the hook density to the desired range for lowdensity hook application. Examples of suitable uses for this low densityhook element, as a tab or patch, are illustrated in FIGS. 15–18. In FIG.15, a large area fastening tab is attached to a carrier substrate 92,which is attached to a diaper 90 as is known in the art. The fasteningtab could be of a size of from 5 to 100 cm², preferably 20 to 70 cm² andcan be attached directly to a low loft nonwoven 95 forming the outercover of the diaper. Typically, this low loft nonwoven would be aspunbond web, a bonded carded or air laid web, a spunlace web or thelike. FIG. 16 is a variation of this fastening tab type construction fora diaper 95, however, where the hook tab 96 is directly bonded to thediaper 95, either at an ear cutout portion or at the edge region of thediaper. FIG. 17 is a further embodiment of a large area hook tab 98 usedwith a pull up type diaper design. In this embodiment, the hook tab 98would engage a suitable mating region 99 on the opposite face of thepull up diaper. Of course, these two elements could be reversed. In bothcases, the mating region could be a nonwoven used to form the nonwovenouter cover of the diaper or the nonwoven fluid permeable topsheet. FIG.18 is an embodiment of the invention hook material being used as a largearea patch 101 on a feminine hygiene article 100. The patch could beused as the primary attachment element to the undergarment, optionally asecondary attachment element 103 could be provided on attachment wings102. The use of the low density hook element as a large area patch couldalso be used on a diaper where the patch could form a part or all of thediaper outer cover.

Suitable polymeric materials from which the hook fastener portion can bemade include thermoplastic resins comprising polyolefins, e.g.polypropylene and polyethylene, polyvinyl chloride, polystyrene, nylons,polyester such as polyethylene terephthalate and the like and copolymersand blends thereof. Preferably the resin is a polypropylene,polyethylene, polypropylene-polyethylene copolymer or blends thereof.

In a preferred embodiment, the orientable thermoplastic resin is blendedwith a material that will form a distinct second phase. The orientablethermoplastic resin constitutes a continuous first phase, generally 50percent or greater by volume of the volume of the blend as extruded. Thethermoplastic resin can be a single resin or a homogeneous or amechanically compatible blend. Compatibility of polymer blends can bedetermined by using differential scanning calorimetry (DSC) to measurethe melting points and glass transition temperatures of the polymerblend. If two glass transition temperatures are detected by DSC due tothe constituent polymers in the blend, the blend is said to beincompatible. If a single glass transition temperature, intermediatebetween those of the component polymers, is detected, the blend is saidto be compatible. Mechanically compatible blends represent a deviationfrom this generality, since they exhibit two glass transitiontemperatures but have finer morphology, are translucent and areextrudable without gross phase separation. Such blends are useful inthis invention. The distinct second phase is generally a discontinuousphase but also could be a continuous phase. The presence of a distinctsecond phase results in substantial increases in the degree of heatshrinkage of the heat treated projection or hook. The distinct secondphase could preferably be a gas, a nonparticulate diluent, a phasedistinct thermoplastic polymer, a tackifier or combination of thesematerials.

Examples of preferred nonparticulate diluents that can be used incombination with the thermoplastic resins include, but are not limitedto, mineral oils, petroleum jelly, low molecular weight polyethylene,soft Carbowax and mixtures thereof Mineral oils are preferred amongthese diluents because of their relatively low cost. The diluents mayoptionally be partially or entirely extracted from the extruded hookfilm by known methods. The diluents can be varied within a wide rangewithin the starting thermoplastic resin used for production of the filmbacked fastener. The amount of diluents used is preferably in the rangeof 20–60% by weight, and more preferably 25–40% by weight of thestarting thermoplastic material. If the amount of diluent added to thestarting material is under 20% by weight, the increase in shrinkage ofthe hook element or projection is reduced, while if it is above 60% byweight it becomes more difficult to produce flexible coherent filmbacked fasteners.

Physical or chemical blowing agents are useful in the present inventionto form distinct gas phases. A blowing agent may be any material that iscapable of forming a vapor at the temperature and pressure at which theextrudate exits the die. A blowing agent may be a physical blowingagent. A physical blowing agent may be introduced, i.e., injected intothe thermoplastic material as a gas or supercritical fluid. Flammableblowing agents such as pentane, butane and other organic materials maybe used, but non-flammable, non- toxic, non-ozone depleting blowingagents such as carbon dioxide, nitrogen, water, SF₆, nitrous oxide,argon, helium, noble gases, such as xenon, air (nitrogen and oxygenblend), and blends of these materials are preferred because they areeasier to use, e.g., fewer environmental and safety concerns. Othersuitable physical blowing agents include, e.g., hydrofluorocarbons(HFC), hydrochlorofluorocarbons (HCFC), and fully- or partiallyfluorinated ethers.

If chemical blowing agents are used, they are preferably added to thethermoplastic resin at a temperature below that of the activationtemperature of the blowing agent, and are typically added to thethermoplastic resin feed at room temperature prior to introduction tothe extruder. The blowing agent is then mixed to distribute itthroughout the polymer in unactivated form, above the melt temperatureof the thermoplastic resin, but below the activation temperature of thechemical blowing agent. Once dispersed, the chemical blowing agent maybe activated by heating the mixture to a temperature above theactivation temperature of the agent. Activation of the blowing agentliberates gas either through decomposition (e.g., exothermic chemicalblowing agents such as azodicarbonamide) or reaction (e.g., endothermicchemical blowing agents such as sodium bicarbonate-citric acidmixtures), such as N₂, CO₂ and/or H₂O, yet cell formation is restrainedby the temperature and pressure of the system. Useful chemical blowingagents typically activate at a temperature of 140° C. or above.

Examples of chemical blowing agents include synthetic azo-, carbonate-,and hydrazide based molecules, including azodicarbonamide,azodiisobutyronitrile, benzenesulfonhydrazide, 4,4-oxybenzenesulfonyl-semicarbazide, p-toluene sulfonyl semi-carbazide, bariumazodicarboxylate, N,N′-dimethyl-N,N′-dinitrosoterephthalamide andtrihydrazino triazine. Specific examples of these materials are CelogenOT (4,4′ oxybis (benzenesulfonylhydrazide)). Other chemical blowingagents include endothermic reactive materials such as sodiumbicarbonate/citric acid bends that release carbon dioxide. Specificexamples include Reedy International Corp SAFOAM products.

When the extrudate exit temperature is at or below 50° C. above theT_(m) of the thermoplastic resin, the increase in T_(m) of the resin asthe blowing agent comes out of the solution causes crystallization ofthe thermoplastic resin, which in turn arrests the growth andcoalescence of the foam cells. When exit temperatures are in excess of50° C. above the T_(m) of the thermoplastic resin, cooling of the resinmay take longer, resulting in non-uniform, unarrested cell growth.

The amount of blowing agent incorporated into the foamable thermoplasticphase is generally chosen to yield a foam having a void content inexcess of 10%, more preferably in excess of 20%, as measured by densityreduction; [1−the ratio of the density of the foam to that of the neatpolymer]×100.

Preferably, the formed foam is oriented such as by uniaxial or biaxialstretching in mutually perpendicular directions at a temperature abovethe alpha transition temperature and below the melting temperature ofthe thermoplastic phase. Foams may be stretched in one or bothdirections 3 to 50 times total draw ratio (MD×CD) for biaxial stretchingor 1–10 times for uniaxial stretching. Generally greater orientation isachievable using foams of small cell size; foams having cell size ofgreater than 100 microns are not readily biaxially oriented more than 20times (MD×CD), while foams having a cell size of 50 microns or lesscould be stretched up to 50 times total draw ratio. In addition foamswith small average cell size exhibit greater tensile strength andelongation to break after stretching. Small cell sizes (100 microns orless) in combination with the orientation allows a foam sheet thicknessof 25 microns to 1000 microns, and foam sheets of 25 microns to 100microns are readily prepared. This is extremely desirable with hookstructures, as a soft conformable backing is obtained that can be usedin many uses where contact with an active wearer (e.g., a person) isdesired or possible. Specifically, the foamed hook can be used withdisposable absorbent articles such as diapers as a closure tab, which issoft to the touch and is aesthetically pleasing due to its pearlescentappearance. Other uses where a hook strip or tab would be in contactwith a sensitive surface would include medical wrap, sport wraps,headbands, produce wraps and feminine hygiene articles. Suitablebackings can have a stiffness of from 10 to 2000 Gurley stiffness units,preferably from 10 to 200 Gurley stiffness units.

Preferably, the foam can have cell sizes of 2 to 100 microns, preferably5 to 50 microns. The foam may alternatively, or additionally, have acell size distribution with a polydispersity from 1.0 to 2.0, preferablyfrom 1.0 to 1.5, more preferably from 1.0 to 1.2.

For forming these foams, the thermoplastic orientable resins arepreferably high melt strength polyolefins, such as branched polyolefins.These high melt strength polymers help control the growth of the foamcells within the desired range necessary for creating the discretemicrostructures and prevent collapse of the cells during surfacemicrostructure formation if needed. Suitable semi-crystalline materialsinclude polyethylene, polypropylene, polymethylpentene, polyisobutylene,polyolefin copolymers, Nylon 6, Nylon 66, polyester, polyestercopolymers, fluoropolymers, poly vinyl acetate, poly vinyl alcohol, polyethylene oxide, functionalized polyolefins, ethylene vinyl acetatecopolymers, metal neutralized polyolefin ionomers available under thetrade designation SURLYN (E. I. DuPont de Nemours, Wilmington, Del.),polyvinylidene fluoride, polytetrafluoroethylene, polyformaldehyde,polyvinyl butyral, and copolymers having at least one semi-crystallinecompound. Preferred high melt strength polymers are high melt strengthpolypropylenes which include homo- and copolymers containing 50 weightpercent or more propylene monomer units, preferably at least 70 weightpercent, and have a melt strength in the range of 25 to 60 cN at 190° C.Melt strength may be conveniently measured using an extensionalrheometer by extruding the polymer through a 2.1 mm diameter capillaryhaving a length of 41.9 mm at 190° C. and at a rate of 0.030 cc/sec; thestrand is then stretched at a constant rate while measuring the force tostretch at a particular elongation. Preferably the melt strength of thepolypropylene is in the range of 30 to 55 cN, as described in WO99/61520.

Such high melt strength polypropylenes may be prepared by methodsgenerally known in the art. Reference may be made to U.S. Pat. No.4,916,198 which describes a high melt strength polypropylene having achain- hardening elongational viscosity prepared by irradiation oflinear propylene in a controlled oxygen environment. Other usefulmethods include those in which compounds are added to the moltenpolypropylene to introduce branching and/or crosslinking such as thosemethods described in U.S. Pat. No. 4,714,716, WO 99/36466 and WO00/00520. High melt strength polypropylene may also be prepared byirradiation of the resin as described in U.S. Pat. No. 5,605,936. Stillother useful methods include forming a bipolar molecular weightdistribution as described in J I Raukola, “A New Technology ToManufacture Polypropylene Foam Sheet And Biaxial Oriented Foam Film”,VTT Publications 361, Technical Research Center of Finland, 1998 and inU.S. Pat. No. 4,940,736.

A second distinct phase can be formed by a blend of two or moreincompatible thermoplastic polymers. Compatibility can be determined byusing differential scanning calorimetry (DSC) to measure the meltingpoints and glass transition temperatures of the polymer blend. If twoglass transition temperatures are detected by DSC due to the constituentpolymers in a blend, the blend is said to be incompatible. If a singleglass transition temperature, intermediate between those of thecomponent polymers, is detected, the blend is said to be compatible.Phase distinct polymer blends can be prepared from blends of olefinicpolymers with non-olefinic polymers. Examples of olefinic polymersinclude polypropylene, polyethylene, propylene-ethylene random andimpact copolymers, polybutenes and polyethylenevinylacetates. Examplesof non-olefinic polymers include polystyrenes, polyamides, polyurethanesand polyesters. Block copolymers such as styrene-isoprene-styrene (SIS)and styrene-ethylenebutylene-styrene (SEBS) are useful as one of theconstituents of the blends.

The backing of the fastener must be thick enough to allow it to beattached to a substrate by a desired means such as sonic welding, heatbonding, sewing or adhesives, including pressure sensitive or hot meltadhesives, and to firmly anchor the stems and provide resistance totearing when the fastener is peeled open. However, when a fastener isused on a disposable garment, the backing should not be so thick that itis stiffer than necessary. Generally, the backing has a Gurley stiffnessof 10 to 2000, preferably 10 to 200 so as to allow it to be perceived assoft when used either by itself or laminated to a further carrierbacking structure such as a nonwoven, woven or film-type backing, whichcarrier backing should also be similarly soft for use in disposableabsorbent articles. The optimum backing thickness will vary dependingupon the resin from which the hook fastener portion is made, but willgenerally be between 20 μm and 1000 μm, and is preferably 20 to 200 μmfor softer backings.

An alternative method for extruding hook members from a die is describedin U.S. Pat. No. 6,209,177 which results in hook fastening portions suchas shown in FIG. 10. Each of the hook members comprises a stem portion41 projecting from the surface of the backing 42 and a hook head 43projecting from an end of the stem portion 41 sideways in at least onedirection. A thickness of the hook member 40, which is perpendicular toa projecting direction of the hook head portion 43 of the hook member40, gradually increases from a top portion of the hook head portion 43toward a rising base end of the stem portion 41. With these hook members40 each hook member 40 is molded independently of each other andintegral with the surface of the backing substrate 42, in contrast tocutting of ribs and drawing of the backing substrate. The molten resinis extruded through a die plate however in this method a face of the dieincludes an ascending/descending member vertically reciprocating insliding contact with a front of the die face interrupting polymer flowto the die elements forming the ridges. During extrusion molding themolten resin constantly forms the base while the ascending anddescending movement of an ascending/descending member interrupts flow tothe rib section resulting in a vertical line of a plurality of separatehook members 40 continuously extending from the backing substrate 42.

The invention microhooks generally have been formed to be particularlyuseful in engaging with low profile nonwoven laminates. Most notablyimproved engagement has been unexpectedly discovered where the hookshave relatively low arm droop, and the ratio of the arm droop to thethickness of the nonwoven portion of a nonwoven laminate is less than1.5, preferably less than 1.3 and most dramatically when less than 1.0.The peel force (135 degree) is generally above 120 grams/2.5 cm,preferably greater than 200 grams/2.5 cm.

Suitable low profile nonwoven laminates are laminates of a nonwovenfabric or web to a film or a higher strength nonwoven fabric or web. A“nonwoven fabric or web” is a web of individual fibers or threads whichare randomly associated fibers that are not associated in a regularmanner such as in a knitted fabric. Nonwoven fabrics or webs can beformed from processes such as, for example, meltblowing, spunbonding,spunlace and bonded carded webs.

In a preferred embodiment, the laminate is a film/nonwoven laminatewhere the nonwoven fabric, preferably a spunbond web, is thermally orextrusion bonded to a film. The film can have a center bonding layerwhich is made from a polymer which more easily bonds to the nonwoven,such as a semi-crystalline/amorphous with a base layer of anotherpolymer, such as a polyolefin. Pigments can also be used in the baselayer.

Suitable bonding layers include polymers such as disclosed in EuropeanPatent Application EP 0444671 A3, European Patent application EP 0472946A2, European Patent Application EP 0400333 A2, U.S. Pat. No. 5,302,454and U.S. Pat. No. 5,368,927 and other bonding polymers includeethylene-n-butyl acetate, ethylene/vinyl acetate copolymers,ethylene/methyl acetate copolymers, ethyl acrylic acid and othercopolymers, and terpolymers of polypropylene, polyethylene andpolybutylene as well as elastomers such as styrene conjugated dieneblock copolymer such as SEBS, SEPS, SBS, and urethanes.

A base layer used with bonding layer may be a polypropylene polymer orcopolymer. Since this layer is relatively thick, the majority of opacityif desired may be added to this layer through the use of opacifiers suchas, for example, TiO₂ or CaCO₃. The nonwoven and the film or higherstrength nonwoven component are preferably bonded together using thermalpoint bonding (heat or ultrasonic bonding). The point bonding if usedshould be at a density that would allow hooks to penetrate into thenonwoven, generally 30 percent or less, and preferably 20 percent orless. The lower bond area limit depends on the integrity of the laminateand the bond strength at the points but it is generally greater than 1to 2 percent. A compatible tackifying resin may also be added to thebonding layer.

The nonwoven used in the laminates preferably is produced by meltblowingor spunbonding processes, which processes are well known in the art. Theextruded fibers were generally deposited on a moving foraminous mat orbelt to form the nonwoven fabric. The fibers produced in the spunbondand meltblown processes have average fiber diameters of less than 75microns and less. Meltblown fibers are able to be produced havingaverage fiber diameter of 10 microns and less, to about 1 micron.Spunbond fibers are generally 25 microns or more and are preferred foruse to engage with the invention microhooks due to their greaterstrength. The nonwoven portion of the laminate generally has a thicknessof from 100 to 300 microns, preferably from 100 to 200 microns and has abasis weight of from 10 to 50 g/m².

Test Methods

135 Degree Peel Test

The 135 degree peel test was used to measure the amount of force thatwas required to peel a sample of the mechanical fastener hook materialfrom a sample of loop fastener material. A 5.1 cm×12.7 cm piece of aloop test material was securely placed on a 5.1 cm×12.7 cm steel panelby using a double-coated adhesive tape. The loop material was placedonto the panel with the cross direction of the loop material parallel tothe long dimension of the panel. A 1.9 cm×2.5 cm strip of the mechanicalfastener to be tested was cut with the long dimension being in themachine direction of the web. A 2.5 cm wide paper leader was attached tothe smooth side of one end of the hook strip. The hook strip was thencentrally placed on the loop so that there was a 1.9 cm×2.5 cm contactarea between the strip and the loop material and the leading edge of thestrip was along the length of the panel. The strip and loop materiallaminate was then rolled by hand, twice in each direction, using a 1000gram roller at a rate of approximately 30.5 cm per minute. The samplewas then placed in a 135 degree peel jig. The jig was placed into thebottom jaw of an Instron™ Model 1122 tensile tester. The loose end ofthe paper leader was placed in the upper jaw of the tensile tester. Acrosshead speed of 30.5 cm per minute and a chart recorder set at achart speed of 50.8 cm per minute was used to record the peel force asthe hook strip was peeled from the loop material at a constant angle of135 degrees. An average of the four highest peaks was recorded in grams.The force required to remove the mechanical fastener strip from the loopmaterial was reported in grams/2.54 cm-width. A minimum of 10 tests wererun and averaged for each hook and loop combination.

Two different loop materials were used to measure the performance of themechanical fastener hook material. Loop material ‘A’ is a nonwoven loopmade similar to that described in U.S. Pat. No. 5,616,394 Example 1,available from the 3M Company as KN-1971. Loop material ‘B’ is a knittedloop made similar to that described in U.S. Pat. No. 5,605,729, Example1 available from the 3M Company as XML-01-160. The loop test materialswere obtained from a supply roll of the material after unwinding anddiscarding several revolutions to expose “fresh” material. The loop testmaterial thus obtained was in a relatively compressed state and was usedimmediately in the peel test before any significant relofting of theloops could occur.

135 Degree Peel Test for Low Profile Loops

A 135 degree peel test was used to measure the amount of force that wasrequired to peel a sample of the mechanical fastener hook material froma sample of low profile loop fastener material. A 1.9 cm×2.5 cm strip ofthe mechanical fastener to be tested was cut with the long dimensionbeing in the machine direction of the web. A 2.5 cm wide paper leaderwas attached to the smooth side of one end of the hook strip. The hookmaterials were fastened to the low profile loop material using thefollowing procedure: The hook material, with hook side down, was placedonto the low profile loop backsheet material of a diaper. A 4.1 kgweight measuring 7.6 cm×7.6 cm with medium grit abrasive paper on thebottom surface, was placed on top of the hook material. To engage thehook with the backsheet loop material, the diaper was held securely flatand the weight was twisted 45 degrees to the right, then 90 degrees tothe left, then 90 degrees right and then 45 degrees left. The weight wasthen removed and the diaper was held firm against the surface of a 135degree jig stand mounted into the lower jaw of an Instron™ Model 1122tensile tester. The loose end of the paper leader attached to the hookmaterial was placed in the upper jaw of the tensile tester. A crossheadspeed of 30.5 cm per minute and a chart recorder set at a chart speed of50.8 cm per minute was used to record the peel force as the hook stripwas peeled from the loop material at a constant angle of 135 degrees. Anaverage of the four highest force peaks was recorded in grams and wasreported in grams/2.54 cm-width. 10 different locations were tested oneach diaper with the average of the 10 being reported in Table 4.

Three different low profile loop materials were used to measure theperformance of the mechanical fastener hook material. Loop material ‘C’is the nonwoven side (i.e. outward facing side) of the backsheet of aLoving Touch diaper size 3. Loop material ‘D’ is the nonwoven side (i.e.outward facing side) of the backsheet of a Walgreens Supreme diaper size4. Loop material ‘E’, was cut from a Leggs Sheer Energy B nylonstocking. The fabric was stretched by hand approximately 200% and thenattached to a 5 cm×15 cm steel panel using double-coated adhesive tape.The thickness of the fabric was measured in the stretched conditionusing an optical microscope. Twelve measurements were averaged to obtaina thickness of 239 microns.

Hook Dimensions

The dimensions of the Example and Comparative Example hook materialswere measured using a Leica microscope equipped with a zoom lens at amagnification of approximately 25×. The samples were placed on a x-ymoveable stage and measured via stage movement to the nearest micron. Aminimum of 3 replicates were used and averaged for each dimension. Inreference to the Example and Comparative Example hooks, as depictedgenerally in FIGS. 5, 6, 7, 11, 12, 13 and 14 hook width is indicated bydistance 23, hook height is indicated by distance 20, arm droop isindicated by distance 24, and hook thickness is indicated by distance21.

Molecular Orientation and Crystallinity

The orientation and crystallinity of the Example and comparative examplehook materials were measured using X-ray diffraction techniques. Datawas collected using a Bruker microdiffractometer (Bruker AXS, Madison,Wis.), using copper K_(α) radiation, and HiSTAR™ 2-dimensional detectorregistry of scattered radiation. The diffractometer was fitted with agraphite incident beam monochromator and a 200 micrometer pinholecollimator. The X-ray source consisted of a Rigaku RU200 (Rigaku USA,Danvers, Mass.) rotating anode and copper target operated at 50kilovolts (kV) and 100 milliamperes (mA). Data was collected intransmission geometry with the detector centered at 0 degrees (2θ) and asample to detector distance of 6 cm. Test specimens were obtained bycutting thin sections of the hook materials in the machine directionafter removing the hook arms. The incident beam was normal to the planeof the cut sections and thus was parallel to the cross direction of theextruded web. Three different positions were measured using a laserpointer and digital video camera alignment system. Measurements weretaken near the center of the head portion 17, near the midpoint of thestem portion 15, and as close as possible to the bottom of the stemportion 17 just slightly above the surface 12 of the backing 11. Thedata was accumulated for 3600 seconds and corrected for detectorsensitivity and spatial linearity using GADDS™ software (Bruker AXSMadison, Wis.). The crystallinity indices were calculated as the ratioof crystalline peak area to total peak area (crystalline+amorphous)within a 6 to 32 degree (2θ) scattering angle range. A value of onerepresents 100 percent crystallinity and value of zero corresponds tocompletely amorphous material (0 percent crystallinity). The percentmolecular orientation was calculated from the radial traces of thetwo-dimensional diffraction data. Background and amorphous intensitieswere assumed to be linear between the 2θ positions defined by traces (A)and (C) defined below. The background and amorphous intensities in trace(B) were interpolated for each element and subtracted from the trace toproduce (B′). Plot of trace (B′) has constant intensity in absence oforientation or oscillatory intensity pattern when preferred orientationpresent. The magnitude of the crystalline fraction possessing nopreferred orientation is defined by the minimum in the oscillatorypattern. The magnitude of the oriented crystalline fraction is definedby the intensity exceeding the oscillatory pattern minimum. The percentorientation was calculated by integration of the individual componentsfrom trace (B′).

Trace (A): leading background edge and amorphous intensity; 12.4–12.8degrees (2θ) radially along χ, 0.5 degree step size.

Trace (B): random and oriented crystalline fractions, backgroundscattering, and amorphous intensity; 13.8–14.8 degrees (2θ) radiallyalong χ, 0.5 degree step size.

Trace (C): trailing background edge and amorphous intensity; 15.4 to15.8 degrees (2θ) radially along χ, 0.5 degree step size.

Trace (B′): random and oriented crystalline fractions obtained bysubtraction of amorphous and background intensity from trace (B).

-   scattering angle center of trace (A): (12.4 to 12.8) deg.=12.6 deg.    2θ-   center of trace (B): (13.8 to 14.8) deg.=14.3 deg. 2θ-   center of trace (C): (15.4 to 15.8) deg.=15.6 deg. 2θ-   Interpolation constant=(14.3−12.6)/(15.6−12.6)=0.57-   for each array element [i]:    Intensity_((amorphous+background)) [i]=[(C[i]−A[i])*0.57]+A[i]    B′[i]=B[i]−Intensity_((amorphous+background)) [i]

From a plot of B′[i] versus [i]:B′_((random)[i]=intensity value of minimum in oscillatory pattern)B′ _((oriented)) [i]=B′[i]−B′ _((random)) [i]Using a Simpson's Integration technique and the following areas thepercent of oriented material was calculated.B′[i]=total crystalline area (random+oriented)=Area_((total))B′_((oriented)) [i]=oriented crystalline area=Area_((oriented))B′_((random)) [i]=random crystalline area=Area_((random))% oriented material=(Area_((oriented))/Area_((total)))×100

COMPARATIVE EXAMPLE C1

A mechanical fastener hook material web was made using the apparatusshown in FIG. 1. A polypropylene/polyethylene impact copolymer(SRC7-644, 1.5 MFI, Dow Chemical) was extruded with a 6.35 cm singlescrew extruder (24:1 L/D) using a barrel temperature profile of 177°C.–232° C.–246° C. and a die temperature of approximately 235° C. Theextrudate was extruded vertically downward through a die having anopening cut by electron discharge machining. After being shaped by thedie, the extrudate is quenched in a water tank at a speed of 6.1meter/min with the water being maintained at approximately 10° C. Theweb was then advanced through a cutting station where the ribs (but notthe base layer) were transversely cut at an angle of 23 degrees measuredfrom the transverse direction of the web. The spacing of the cuts was305 microns. After cutting the ribs, the base of the web waslongitudinally stretched at a stretch ratio of approximately 4.1 to 1between a first pair of nip rolls and a second pair of nip rolls tofurther separate the individual hook elements to approximately 8hooks/cm. There were approximately 10 rows of ribs or cut hooks percentimeter. The upper roll of the first pair of nip rolls was heated to143° C. to soften the web prior to stretching. The general profile ofthis hook is depicted in FIG. 5.

EXAMPLE 1

The web of comparative example C1 was subjected to a non-contact heattreatment on the hook side of the web by passing said web underneath a36 cm wide ribbon flame burner Aerogen (Alton Hampshire, UK) at a speedof 90 meter/minute with a burner to film gap of 8 mm. The flame powerwas 74 kJ/hour. The smooth base film side of the web was supported on achill roll maintained at approximately 18° C. The general profiles ofthe resulting heat treated hook are depicted in FIGS. 6 a and 6 b. Theperformance of the hook material web against nonwoven loop material ‘A’was measured using a 135° peel test with the results shown in Table 1below. The peel force of the heat-treated web was approximately 63%greater than the non-heated Comparative Example 1.

EXAMPLE 2

The web of Comparative Example C1 was subjected to a non-contact heattreatment on the hook side of the web by passing said web underneath abank of 6–1000 watt 1 micron wavelength infrared bulbs at a speed of 2.1meter/min. The hook to bulb spacing was approximately 2.5 cm. The smoothbase film side of the web was supported on a chill roll maintained atapproximately 66° C. The general profiles of the resulting heat treatedhook are depicted in FIGS. 7 a and 7 b. The performance of the hookmaterial web against nonwoven loop material ‘A’ was measured using apeel test with the results shown in Table 1 below. The 135° peel forceof the heat-treated web was approximately 206% greater than the non-heattreated Comparative Example C1.

COMPARATIVE EXAMPLE C2

A mechanical fastener hook material web was made as in ComparativeExample 1 except the web was extruded at a speed of 9.1 meter/min toincrease the amount of melt flow induced molecular orientation in theextrudate. The general profile of this hook is depicted in FIG. 5.

EXAMPLE 3

The web of Comparative Example C2 was subjected to a non-contact heattreatment on the hook side of the web by passing said web underneath abank of 6–2000 watt 1 micron wavelength infrared bulbs at a speed of 3.0meter/min. The hook to bulb spacing was approximately 1.6 cm. The smoothbase film side of the web was supported on a chill roll maintained atapproximately 66° C. The performance of the hook material web againstnonwoven loop material ‘A’ was measured using a peel test with theresults shown in Table 1 below. The 135° peel force of the heat-treatedweb was approximately 37% greater than the non-heat treated ComparativeExample C2.

COMPARATIVE EXAMPLE C3

A mechanical fastener hook material web was made as in ComparativeExample 1 except the extrudate was pulled from the die lip at a 20degree angle from vertical so as to produce a cross-sectional profile asshown in FIG. 11. Hook spacing was 16 rows of hooks per centimeter.

EXAMPLE 4

The web of Comparative Example C3 was subjected to a non-contact heattreatment on the hook side of the web by passing said web underneath abank of 3–4500 watt 3 micron wavelength infrared bulbs at a speed of10.0 meter/min producing hook members such as shown in FIG. 11 with ahook head portion 77 and stem portion 75 and a base 73. The hook to bulbspacing was approximately 2.5 cm. The smooth base film side of the webwas supported on a chill roll maintained at approximately 66° C. Theperformance of the hook material web against nonwoven loop material ‘A’was measured using a 135° peel test with the results shown in Table 1below. The peel force of the heat-treated web was approximately 254%greater than the non-heat treated Comparative Example C3.

EXAMPLE 5

The web of Comparative Example C3 was subjected to a non-contact heattreatment on the hook side of the web by passing said web underneath aperforated metal plate at a speed of 25.0 meter/min producing hookmembers having a profile substantially as shown in FIG. 11. Hot air at atemperature of approximately 185° C., provided by a 15 kW electricheater, was blown through the perforations in the metal plate onto thehook side of the web at a velocity of approximately 3350 meter/min. Thehooks were approximately 46 cm from the perforated plate. The smoothbase film side of the web was supported on a chill roll at approximately149° C. After heat treatment the web was cooled by passing the web overa chill roll maintained at 11° C. The performance of the hook materialweb against nonwoven loop material ‘A’ was measured using a 135° peeltest with the results shown in Table 1 below. The peel force of theheat-treated web was approximately 136% greater than the non-heattreated Comparative Example C3.

COMPARATIVE EXAMPLE C4

A mechanical fastener hook material web was made as in comparativeexample 1 except the opening in the die was shaped as shown in FIG. 14(after heat treating) and the spacing of the cuts was 267 microns priorto stretching the web.

EXAMPLE 6

The web of comparative example C4 was subjected to a non-contact heattreatment on the hook side of the web by passing said web underneath abank of 3–4500 watt 3 micron wavelength infrared bulbs at a speed of10.0 meter/min producing hook members 90 such as shown in FIG. 14. Thehook to bulb spacing was approximately 2.5 cm. The smooth base film sideof the web was supported on a chill roll maintained at approximately 66°C. The performance of the hook material web against nonwoven loopmaterial ‘A’ and knitted loop material ‘B’ was measured using a 135°peel test with the results shown in Table 1 below. The peel force of theheat-treated web using loop material ‘A’ was approximately 112% greaterthan the non-heat treated Comparative Example C4 and 32% greater whenusing loop material ‘B’.

COMPARATIVE EXAMPLE C5

A mechanical fastener hook material web was made as in ComparativeExample 1 except a high density polyethylene resin (D450 4.5 MI, 0.942density, Chevron Philips) blended with 2% MB50 silicone/PP masterbatch(Dow Corning) processing aid was used to form the extrudate at a melttemperature of approximately 238° C. The opening in the die was shapedto produce the profile 80 depicted in FIG. 12. After quenching theextrudate and cutting of the ribs the web was oriented in the machinedirection 3.5:1.

COMPARATIVE EXAMPLE C6

A mechanical fastener hook material web, available from the 3MCorporation as KN-3425, was made similar to Comparative Example 1. Thedimensions of the hook material are shown in Table 3.

EXAMPLE 7

The web of Comparative Example C5 was subjected to a non-contact heattreatment on the hook side of the web by passing said web underneath abank of 6–2000 watt 1 micron wavelength infrared bulbs at a speed of 4.0meter/min producing hook member 85, substantially as shown in FIG. 13.The hook to bulb spacing was approximately 1.6 cm. The smooth base filmside of the web was supported on a chill roll maintained atapproximately 66° C. The performance of the hook material web againstnonwoven loop material ‘A’ was measured using a 135° peel test with theresults shown in Table 1 below. The peel force of the heat-treated webwas approximately 151% greater than the non-heat treated ComparativeExample C5.

EXAMPLE 8

A web was made similar to Comparative Example C3 except the extrudatewas pulled from the die lip at a 20 degree angle from vertical so as toproduce a slightly different cross-sectional profile. The web wassubjected to a non-contact heat treatment on the hook side of the web bypassing said web underneath a perforated metal plate at a speed of 25.0meter/min producing hook members having a profile substantially as shownin FIG. 11. Hot air at a temperature of approximately 185° C., providedby a 15 kW electric heater, was blown through the perforations in themetal plate onto the hook side of the web at a velocity of approximately3350 meter/min. The hooks were approximately 46 cm from the perforatedplate. The smooth base film side of the web was supported on a chillroll at approximately 149° C. After heat treatment the web was cooled bypassing the web over a chill roll maintained at 11° C. The dimensions ofthe resulting heat-treated hook material are shown in Table 3 below andthe peel performance against low profile loops is shown in Table 4. Thepeel force of the heat-treated web was approximately 62% and 60% greaterrespectively, for low profile loops ‘C’ and ‘D’, than the non-heattreated Comparative Example C6.

EXAMPLE 9

A web was made similar to Comparative Example C3 except the extrudatewas pulled vertically from the die lip. The web was subjected to anon-contact heat treatment on the hook side of the web by passing saidweb underneath a perforated metal plate at a speed of 25.0 meter/minproducing hook members having a profile substantially as shown in FIG.11. Hot air at a temperature of approximately 185° C., provided by a 15kW electric heater, was blown through the perforations in the metalplate onto the hook side of the web at a velocity of approximately 3350meter/min. The hooks were approximately 46 cm from the perforated plate.The smooth base film side of the web was supported on a chill roll atapproximately 149° C. After heat treatment, the web was cooled bypassing the web over a chill roll maintained at 11° C. The dimensions ofthe resulting heat-treated hook material are shown in Table 3 below andthe peel performance against low profile loops is shown in Table 4. Thepeel force of the heat-treated web was approximately 140% and 107%greater respectively, for low profile loops ‘C’ and ‘D’, than thenon-heat treated Comparative Example C6.

EXAMPLE 10

A web was made similar to Comparative Example C3 except a different dieplate was used to produce a tapered stem having a larger width at thebase of the stem than at the top of the stem. The web was subjected to anon-contact heat treatment on the hook side of the web using thefollowing procedure. A 13 cm×43 cm piece of web was placed onto a 13cm×43 cm steel plate(1.3 cm thick), hook-side up, and edge clamped toprevent the web from shrinking. Hot air from a Master brand hot air gunat 400° C. was blown vertically down onto the web by passing the air gununiformly over the web for about 10 seconds. The dimensions of theresulting heat-treated hook material are shown in Table 3 below and thepeel performance against low profile loops is shown in Table 4. The peelforce of the heat-treated web was approximately 321% and 177% greaterrespectively, for low profile loops ‘C’ and ‘D’, than the non-heattreated Comparative Example C6.

EXAMPLE 11

A web was made similar to the web of Comparative Example C1 except thebase of the web was longitudinally stretched at a stretch ratio ofapproximately 3.65 to 1 between a first pair of nip rolls and a secondpair of nip rolls to further separate the individual hook elements toapproximately 8.5 hooks/cm. There were approximately 15 rows of ribs orcut hooks per centimeter. The web was then subjected to a non-contactheat treatment on the hook side of the web by passing said webunderneath a perforated metal plate at a speed of 8.9 meter/minproducing hook members having a profile similar to those in Example 9and shown in FIG. 11. Hot air at a temperature of approximately 185° C.,provided by a 15 kW electric heater, was blown through the perforationsin the metal plate onto the hook side of the web at a velocity ofapproximately 3350 meter/min. The hooks were approximately 46 cm fromthe perforated plate. The smooth base film side of the web was supportedon a chill roll at approximately 149° C. After heat treatment the webwas cooled by passing the web over a chill roll maintained at 11° C.

EXAMPLE 12

A web was made similar to the web of Example 11 except the web waslongitudinally stretched at a stretch ratio of approximately 2.5 to 1between a first pair of nip rolls and a second pair of nip rolls priorto the cutting step to increase orientation of the web prior to cuttingof the ribs. The upper roll of the first pair of nip rolls was heated to143° C. to soften the web prior to stretching. After stretching, the webwas cut as in Example 11 and then longitudinally stretched at a stretchratio of approximately 3.65 to 1 between a first pair of nip rolls and asecond pair of nip rolls to further separate the individual hookelements to approximately 8.5 hooks/cm. The web was then subjected to anon-contact heat treatment on the hook side of the web as described inExample 11.

TABLE 1 Hook Hook Arm Hook Peel Force Peel Force Hook width Height DroopThickness Loop ‘A’ Loop ‘B’ Material (μm) (μm) (μm) (μm) (grams) (grams)C1 536 573 217 340 202 — 1 663 582 301 85 329 — 2 682 606 341 179 619 —C2 479 512 147 309 164 — 3 703 678 229 133 225 — C3 395 514 128 274 270— 4 483 641 193 171 955 — 5 481 665 172 180 638 — C4 611 819 262 257 382541 6 774 992 399 154 811 716 C5 448 500 143 341 186 — 7 547 526 174 201466 —

Comparative Example C2 and Example 3 were measured to show the change inmolecular orientation and crystallinity due to heat treatment of thewebs of the invention. The results are shown in Table 2 below. When heatis applied to the oriented hook elements, the molecular orientationdecreases dramatically from the top down to the base, and crystallinityincreases due to annealing effects.

TABLE 2 Crystalline % Molecular % Molecular % Molecular IndexOrientation Orientation Orientation Hook Material (top) (top) (body)(base) C2 0.30 36.3 52.0 85.6 3 0.39  0.0  0.0 80.4

EXAMPLE 13

To obtain a fastener web having low hook density, a web was made similarto the web of Example 9 except C104 polypropylene/polyethylene impactcopolymer (1.2 MFI, Dow Chemical, Midland, Mich.) was used as theextrudate. A white color concentrate (50:50 TiO2/PP) was added to theextruder at a 1% loading. The web was quenched and cut as in Example 9.The general profile of the individual hook elements is shown in FIG. 11.The web was then subjected to a biaxial stretching (2×2) using a KARO 4pantograph stretcher (Bruckner GmbH). A 115 mm×115 mm sample of the webwas preheated at a temperature of 130° C. for 60 seconds followed by 2×2stretching at a stretch rate of 100%/second. The hook spacing in themachine direction was approximately 21.3 hooks/cm and 7 hooks/cm in thecross direction. The web was then subjected to a non-contact heattreatment on the hook side of the web using the following procedure. A13 cm×43 cm piece of web was placed onto a 13 cm×23 cm steel plate (1.3cm thick), hook-side up, and edge clamped to prevent the web fromshrinking. Hot air from a 14.5 amperage Master brand hot air gun at 400°C. with a vent setting of 50%, was blown vertically down onto the web bypassing the air gun uniformly over the web for about 20 seconds. Thedimensions of the resulting heat-treated hook material are shown inTable 3 below.

EXAMPLE 14

To obtain a fastener web having even lower hook density, a web was madesimilar to the web of Example 13 except the web was subjected to a 3×3biaxial stretching using a KARO 4 pantograph stretcher. The hook spacingin the machine direction was approximately 12.3 hooks/cm and 4.3 hook/cmin the cross direction. The dimensions of the resulting heat-treatedhook material are shown in Table 3 below.

Table 3 below shows the effect of non-contact heat treatment on hookdimensions. Hook thickness decreases dramatically upon the applicationof heat to hooks having significant molecular orientation.

TABLE 3 Hook Stem Stem Hook Hook Arm Thick- Hooks/ Width Width Hookwidth Height Droop ness cm (base) (top) Material (μm) (μm) (μm) (μm) CD(μm) (μm) C6 521 485 246 343 10 232 231  8 487 511 176 101 14 233 242  9544 426 136 98 14.2 227 279 10 384 645 112 122 18.9 247 153 11 470 555113 143 14.7 240 228 12 449 487 117 70 23.8 196 217 13 571 617 135 947.0 — — 14 607 617 132 113 4.3 — —Thicknesses of the low profile loops ‘C’ and ‘D’ were determined fromscanning electron microscopic (SEM) photos. The nonwoven diaperbacksheets were carefully cut with a razor and SEM photos were taken ofthe cross-section. The distance from the loop/film interface to the topof the loop pile was measured with a ruler from the photographs andconverted to microns. Three locations were measured for three differentreplicates. The nine readings were averaged and are reported below.

Table 4 below shows that as the ratio of hook arm droop to loopthickness decreases, the peel force to thin, low profile nonwoven loopsincreases dramatically.

TABLE 4 Loop Thickness Arm Droop/Loop Peel Force (μm) Thickness Ratio(gms/2.5 cm) Hook Loop Loop Loop Loop Loop Loop Loop Loop Loop MaterialC D E C D E C D E C6 133 154 239 1.85 1.6 1.03 78 110 308  8 133 154 2391.32 1.14 0.74 126 176 409  9 133 154 239 1.02 0.88 0.57 187 228 533 10133 154 239 0.84 0.73 0.47 328 305 542

Table 5 below shows the peel force of low hook density examples 13 and14 peeled from low profile nonwoven loop ‘C’ using the 135 Degree PeelTest for Low Profile Loops described above. The actual number ofindividual hooks per tab was calculated and then divided into the peelforce to obtain the peel force per individual hook member.

TABLE 5 Hook Peel Force Loop # Hooks/ Peel Force/individual Material ‘C’(grams/2.54 cm) test tab hook (grams/hook) 13 152 722 0.21 14 116 2560.51

CONTROL EXAMPLE 15

A mechanical fastener hook material web was made using the apparatusshown in FIG. 1. A polyethylene resin (DFDB 6005, 0.2 MFI, 0.92 density,Dow Chemical Corp., Midland, Mich.) pigmented with 1% TiO₂ colorconcentrate (15100P, Clariant Corp., Minneapolis, Minn.) was extrudedwith a 6.35 cm single screw extruder (24:1 L/D) using a barreltemperature profile of 177° C.–232° C.–246° C. and a die temperature ofapproximately 235° C. The extrudate was extruded vertically downwardthrough a die having an opening cut by electron discharge machining.After being shaped by the die, the extrudate was quenched in a watertank at a speed of 6.1 meter/min with the water being maintained atapproximately 10° C. The web was then advanced through a cutting stationwhere the ribs (but not the base layer) were transversely cut at anangle of 23 degrees measured from the transverse direction of the web.The spacing of the cuts was 305 microns. After cutting the ribs, thebase of the web was longitudinally stretched at a stretch ratio ofapproximately 3 to 1 between a first pair of nip rolls and a second pairof nip rolls to further separate the individual hook elements toapproximately 10 hooks/cm. There were approximately 15 rows of ribs orcut hooks per centimeter. The upper roll of the first pair of nip rollswas heated to 100° C. to soften the web prior to stretching. The generalprofile of this hook is depicted in FIG. 11. The web was then subjectedto a non-contact heat treatment on the hook side of the web using thefollowing procedure. A 13 cm×43 cm piece of web was placed onto a 13cm×43 cm steel plate (1.3 cm thick), hook-side up, and edge clamped toprevent the web from shrinking. Hot air from a Master brand hot air gunat 400° C. was blown vertically down onto the web by passing the air gununiformly over the web for about 10 seconds. The width (thickness) ofthe hooks was measured before and after heat treating and is shown inTable 6 below.

EXAMPLE 16

A hook web was made similar to that of Control Example 15 except 50%polypropylene/polyethylene impact copolymer (C104 1.2 MFI, Dow ChemicalCorp., Midland, Mich.) was blended with the DFDB 6005 polyethyleneresulting in a composition of PE:PP/PE:TiO2 concentrate (15100P) in aratio of 49.5:49.5:1.0. The web was heat treated in the same manner asControl Example 15. The decrease in hook thickness after heat treatmentof the blended hook material was 9.1% greater than the non-blended hookmaterial.

CONTROL EXAMPLE 17

A hook web was made similar to that of Control Example 15 except 99%polypropylene/polyethylene impact copolymer (C104) pigmented with 1%TiO₂ color concentrate (15100P) was used as the extrudate. The die plateused was described in Example 10. The spacing of the cuts was 250microns. The web was heat treated in the same manner as Control Example15. The performance of the hook material web against nonwoven loopmaterial ‘A’ was measured using a peel test with the results shown inTable 6 below.

EXAMPLE 18

A hook web was made similar to that of Control Example 17 except 10% SISblock copolymer (KRATON 1119, Kraton Polymers, Houston, Tex., USA) wasblended with the C104 polypropylene resulting in a composition ofPP:SIS:TiO₂ concentrate (15100P) in a ratio of 89:10:1. The web was heattreated in the same manner as Control Example 17. The decrease in hookthickness after heat treatment of the blended hook material was 7.5%greater than the non-blended hook material. The 135° peel force of theheat-treated blended web was approximately 68% greater than thenon-blended Control Example 17.

CONTROL EXAMPLE 19

A hook web was made similar to that of Control Example 15 except 99%polypropylene/polyethylene impact copolymer (SRC-7644, Dow Chemical Co.,Midland, Mich.) pigmented with 1% TiO₂ color concentrate (15100P) wasused as the extrudate and different cutting conditions were used toproduce a thicker hook. The web was heat treated in the same manner asControl Example 15. The performance of the hook material web againstnonwoven loop material ‘A’ was measured using a 135° peel test with theresults shown in Table 6 below.

EXAMPLE 20

A hook web was made similar to that of Control Example 19 except 5%KRATON 1119, 5% FORAL NC tackifier (Hercules Chemical, Wilmington, Del.)and 1% 15100P TiO₂ was blended with 89% SRC-7644polypropylene/polyethylene impact copolymer to form the extrudate. Theweb was heat treated in the same manner as Control Example 15. Thedecrease in hook thickness after heat treatment of the blended hookmaterial was 13.4% greater than the non-blended hook material. The 135°peel force of the heat-treated blended web was approximately 63% greaterthan the non-blended Control Example 19.

EXAMPLE 21

A hook web was made similar to that of Example 20 except a precompoundedresin blend consisting of 65% 5D45 polypropylene (0.7 g/min MFI, DowChemical Co., Midland, Mich.), 35% mineral oil (Superla White No. 31,Chevron Texaco, San Ramon, California, USA) and 0.1% Millad 3988nucleating agent (Milliken Chemical Co., Inman S.C.) was to form theextrudate. The web was heat treated in the same manner as ControlExample 15. The decrease in hook thickness after heat treatment of theblended hook material was 69.3%.

EXAMPLE 22

A hook web was made similar to that of Control Example 17 except acoextrusion process was used to produce a web wherein the hook railswere foamed and the base film layer was unfoamed. A blend of 49% C104copolymer, 49% FH3400 polypropylene and 2% chemical blowing agentconcentrate (FM1307H) was extruded with a 3.8 cm single screw extruder(28:1 L/D) using a “humped” barrel temperature profile of 135° C.–210°C.–177° C. to form the hook rails. 100% 7C06 impact copolymer (UnionCarbide Corp., Danbury, Conn.) was used to form the non-foamed base filmlayer and was extruded with a 6.35 cm single screw extruder (24:1 L/D)using a sloped barrel profile of 204° C. in the feed zone to 232° C. inthe last zone. The melt streams of the two extruders were fed to a threelayer coextrusion feedblock (Cloeren Co., Orange, Tex.) with the thirdlayer inlet blocked such that a two layer output resulted. The feedblockwas mounted onto an extrusion die equipped with a profiled die lip. Thefeedblock and die were maintained at 204° C. After being shaped by thedie lip, the extrudate was quenched in a water tank at a speed of 4.6meter/min with the water being maintained at approximately 16° C.–20° C.The resulting structure had a non-foamed base film layer with upstandinghook rails that were foamed approximately 70% of their height asmeasured from the top downward towards the base. The resulting structurehad a 10% overall void content. The mean cell size of the foam cells inthe foamed portion was 50 microns. The web was then advanced through acutting station where the ribs (but not the base layer) weretransversely cut at an angle of 23 degrees measured from the transversedirection of the web. The spacing of the cuts was 250 microns. Aftercutting the ribs, the base of the web was longitudinally stretched at astretch ratio of approximately 3 to 1 between a first pair of nip rollsand a second pair of nip rolls to further separate the individual hookelements to approximately 10 hooks/cm. The upper roll of the first pairof nip rolls was heated to 100° C. to soften the web prior tostretching. There were approximately 15 rows of ribs or cut hooks percentimeter. The base film layer had a thickness of approximately 75microns. The web was heat treated in the same manner as Control Example15. The decrease in hook thickness after heat treatment of the hookmaterial was 75%. The performance of the hook material web againstnonwoven loop material ‘B’ was measured using a 135° peel test for lowprofile loops with the results shown in Table 6 below. The 135° peelforce of the heat-treated foamed web was approximately 82% greater thanthe non-heat treated foamed web.

TABLE 6 Initial Heat Treated % Change Peel Force Peel Force Hook Hook inHook Loop ‘A’ Loop ‘B’ Hook Thickness Thickness Thickness (grams/(grams/ Material (μm) (μm (μm) 2.5 cm) 2.5 cm) Control 15 281 144 48.716 292 123 57.8 Control 17 254 146 42.4 419 18 254 129 49.5 706 Control19 330 143 56.6 550 20 330 98 70.0 896 21 336 103 69.3 22 305 76 75 209

1. A method of forming a unitary fastener comprising the steps ofextruding a thermoplastic resin in a machine direction through a dieplate having a continuous base portion cavity and one or more ridgecavities extending from the base portion cavity, the extrusion beingsufficient to induce melt flow molecular orientation in the polymerflowing through at least the ridge cavities forming a base portion withridges, forming projections from the thermoplastic resin extrudedthrough the ridge cavities, and subsequently heat treating at least aportion of the solidified projections at a temperature, near or abovethe thermoplastic resin melt temperature, and time sufficient to reducethe thickness of at least an upper portion of the projections by from 5to 90 percent.
 2. The method of forming unitary fasteners of claim 1wherein the projections are hook form projections having a stem portionand a head portion.
 3. A method for forming unitary hook fasteneraccording to claim 2 wherein the formed hooks are heated at atemperature and time sufficient to shrink at least a portion of the hookhead portions of the hook portions by from 5 to 90 percent.
 4. A methodfor forming unitary hook fastener according to claim 3 wherein at leasta portion of the hook head portions are skunk by at least 30 percent. 5.A method for forming unitary hook fastener according to claim 1 whereinthe hook portions are formed by extruding continuous ridges having aprofile of the hook element, on a base portion comprising a film cuttingthe ridges and subsequently stretching the base layer to separate theindividual cut ridges into discrete hook portions.
 6. A method forforming unitary hook fastener according to claim 5 wherein thecontinuous ridges are stretched in the direction of the ridges prior tocutting of the ridges.
 7. The method for forming a unitary hook fasteneraccording to claim 1 wherein the thermoplastic resin is a phase distinctblend of a first continuous phase of thermoplastic resin and a seconddistinct phase.
 8. The method for forming a unitary hook fasteneraccording to claim 1 wherein said second distinct phase is anonparticulate filler.
 9. The method for forming a unitary hook fasteneraccording to claim 8 wherein said filler is a nonparticulate fillercomprising from 20 to 50 percent by volume of the polymeric resin. 10.The method for forming a unitary hook fastener according to claim 1wherein said second phase is a gas.
 11. The method for fanning a unitaryhook fastener according to claim 1 wherein said second phase is adistinct incompatible polymer phase.